Fuses are widely used in electrical equipment connected in series to protect conductors and components from damage due to high current levels (“overcurrent”). Typically, a fuse consists of a fusible link installed in a circuit. When the current in the circuit reaches a predetermined maximum level provided by the fusible link, the fusible link melts or burns (i.e., blows). This breaks the circuit connection provided by the link and terminates the flow of overcurrent in the circuit.
Once the condition causing the overcurrent is corrected, the fuse must be replaced in order to allow current to flow through the fuse and its associated circuitry. Many forms of fuse mounting apparatus have been developed for this purpose.
In many forms of consumer electronics, for example, a cylindrical fuse holder penetrates the electronic unit housing. A removable fuse holder cap extends outwardly from the housing (and unshielded by the housing as well). A tubular fuse is disposed in the cylindrical interior fuse passage in the fuse holder. Electrical contacts at each end of the fuse abut mating contacts at opposing ends of the fuse passage. When the removable cap is removed, the fuse may be readily removed from the cylindrical fuse passage, inspected to determine if it is blown, and replaced if necessary.
A common fuse apparatus in automotive applications provides a fuse block holding a plurality of U-shaped fuses in one location for a number of circuits. In this type of fuse apparatus, the circuitry protected by each fuse remains may or may not be protected by enclosures, such as the engine compartment or a dash board. This centralized fuse location, however, simplifies the task of replacing a fuse since a user does not have to gain access to the protected circuitry. Although this centralized fuse apparatus provides more convenient access to fuses in the apparatus, the user must still test or remove and observe a given fuse to determine if it is blown and the cause of a problem in associated circuitry.
In many other applications, these types of prior art fusing and fuse-access schemes are unsuitable. In many instances, the size or current capacity of the fuse does not lend itself to these types of fuse arrangements. In many of these types of applications, the fuses are mounted on a circuit board within and enclosed by the electronic equipment housing, so that the fuses may be both well shielded and located relatively adjacent to or within the circuit(s) they protect within the housing.
These types of internally mounted fuses (with one or more fuses mounted within the confines of a closed housing) are not easily inspected or accessed. In order to do so, the housing of the unit in which the fuses are mounted must be fully opened by removing a side or top or bottom panel in the housing.
In many cases, the unit must first be removed from an equipment rack in order to be able to open the housing in this fashion and obtain access to the interior of the housing. Then, after inspecting one or more fuses mounted in the housing, the housing must be reassembled and re-mounted in the rack.
Often, an internally fused electronic apparatus will have a warranty provision voiding the warranty if the user opens the equipment housing. A user of this type of equipment therefore cannot even inspect a fuse, much less gain access to it for removal or replacement, without voiding the warranty. Instead, the user must typically obtain a return material authorization from the vendor, ship the unit to the vendor's repair facility for service, and then have the repair facility again ship the unit back to the user—all simply to inspect, and if necessary, replace one or more blown fuses in the unit.
These types of fuse access problems have long been quite predominant in the case of rack mounted systems in which system components are connected to a power distribution unit (PDU) that supplies power to the components in the rack. PDU-supplied rack mounted systems are common in broadcast network head ends and reception/re-broadcast stations, telecommunications central offices, and data centers for local and wide area networks. Components of rack systems can include servers, routers, satellite receivers, amplifiers, codecs (coder/decoders), and cooling equipment.
In these types of environments, the PDU often has a number of power output receptacles mounted in a rectangular housing. The rectangular housing can be mounted adjacent an electronic equipment rack structure (typically outside the confines the rack such as the outside face of a vertical support in the rack), and electronic components in the rack have power supply cords plugged into the power output receptacles in the PDU.
The PDU typically has a number of fuses, each providing overcurrent protection to one or more power output receptacles and electronic equipment plugged into the receptacles. Most commonly, the fuses in this type of PDU are mounted in fuse holders mounted directly to circuit boards within the PDU housing. The fuses can only be inspected and accessed by first unplugging the associated electronic equipment (forcing the equipment to shut down), removing the PDU from the rack if mounted on it, and then opening the PDU housing by removing a top or bottom cover. Removal of the printed circuit board may even be necessary. After inspection and replacement of blown fuses if necessary, the entire process is reversed in order to return the PDU and associated equipment to operational status.
This situation has long prevailed notwithstanding the substantial downtime, problems, costs, and delays that follow from having fuses mounted in this fashion within the PDU and other electronic equipment, particularly heavy duty industrial PDU's and electronic equipment manufactured in compliance with standards requiring particularly low levels of radio frequency or other emissions from the equipment. These problems are particularly problematic in industrial polyphase power supply systems, in which fuses may blow more frequently.
The applicants believe that conventional PDU's have long presented other problems as well. For example, as noted above prior art PDU's are often mounted outside the confines of the rack housing by securing the PDU to the outside surface of a portion of the rack. Wiring between the PDU and associated electronic equipment is therefore exposed outside the confines of the rack and subject to accidental and potentially interrupting or damaging contact with other structures or personnel passing by the rack and associated PDU. When such contact occurs, which it does in practice, electronic equipment can be accidentally shut down or even damaged, and the time required to locate and resolve the problem can be substantial and costly for the operator and its customers or other users.